In the treatment of visual acuity deficiencies, correction by means of eyeglasses or contact lenses are used by a large percentage of the population. Such deficiencies include patients having hyperopia or being far-sighted, myopia or near-sighted patients as well as astigmatisms caused by asymmetry of the patient's eye. More recently, to alleviate the burden of wearing eyeglasses and/or contact lenses, surgical techniques have been developed for altering the shape of the patient's cornea in an attempt to correct refractive errors of the eye. Such surgical techniques include photorefractive keratectomy (PRK), LASIK (laser in-situ keratectomy), as well as procedures such as automated lamilar keratectomy (ALK) or others. These procedures are intended to surgically modify the curvature of the cornea to reduce or eliminate visual defects. The popularity of such techniques has increased greatly, but still carries the risk in both the procedure itself as well as post surgical complications.
An alternative to permanent surgical procedures to alter the shape of the cornea include orthokeratology, where a contact lens is applied to the eye to alter the shape or curvature of the cornea by compression of the corneal surface imparted by the lens. The reshaping of the cornea in orthokeratology has been practiced for many years, but typically has required an extensive period of time to reshape the cornea. It is also typical of orthokeratology treatment plans that the lenses used for reshaping of the cornea be custom designed and manufactured, thereby greatly increasing the cost and complicating the general use of such procedures. Further, orthokeratology lenses typically have various deficiencies, particularly relating to properly designing a lens for a particular patient to achieve best results in the treatment process. For correction of myopia, the design of prior orthokeratology lenses have typically included a base curve at the central portion of the lens for imparting reshaping pressure to the cornea. An annular zone adjacent the base curve, having a curvature being steeper (shorter radius) than the curvature of the base curve, is provided to transition to a peripheral curve used to facilitate centering the lens. This design is referred to as a “reverse geometry” contact lens. These curves were designed to have coaxial geometry, with the origin of each curve maintained on a central axis. The reverse geometry is provided to facilitate comfort in wearing the lens, and to promote tear flow and oxygen transmission to the central cornea under the base curve. The use of a first annular zone about the base curve with a steeper curvature allows the lens surface to be brought into a position near the surface of the cornea in this region, from the flatter central base curve. The use of a steeper curvature in the first annular zone creates design problems in matching the base curve and peripheral curve of the lens, to provide desired reshaping as well as tear flow.
Another deficiency of prior ortho-K lenses is found in the complexity of the designs, which exacerbate the fitting problems mentioned previously. In the fitting process, if there is an aspect of the lens design, which is not properly fitted for the desired treatment of the patient's eye, or causes excessive discomfort to the patient, the lens must be redesigned accordingly. Unfortunately, in an attempt to redesign a lens, a practitioner may affect other aspects of the lens due to the interdependency between design features. It would be worthwhile to provide an ortho-K lens having independent features, which could be easily modified if required to attain a proper fit in a simpler and more cost-effective process.